U.S. patent application number 14/226978 was filed with the patent office on 2014-10-02 for method and system for detecting a leak in a pipeline.
This patent application is currently assigned to ExxonMobil Research and Engineering Company. The applicant listed for this patent is Mohan G. Kulkarni, Yibing Zhang. Invention is credited to Mohan G. Kulkarni, Yibing Zhang.
Application Number | 20140290343 14/226978 |
Document ID | / |
Family ID | 51619485 |
Filed Date | 2014-10-02 |
United States Patent
Application |
20140290343 |
Kind Code |
A1 |
Kulkarni; Mohan G. ; et
al. |
October 2, 2014 |
METHOD AND SYSTEM FOR DETECTING A LEAK IN A PIPELINE
Abstract
System and method for detecting a leak in a pipeline with a
sensing cable including an optical fiber sensor array aligned with
a heating element. At least one heat pulse is propagated through
the heating element along at least a portion of the sensing cable
to affect an exchange of thermal energy between the heating element
and fluid exposed to the sensing cable. A temperature profile of
the sensing cable corresponding to the heat pulse at each of a
plurality of sensor locations on the optical fiber sensor array is
measured over time. A leak in a pipeline is detected by determining
one or more properties of the fluid exposed to the sensing cable at
each of the plurality of sensor locations based on the temperature
profile corresponding thereto.
Inventors: |
Kulkarni; Mohan G.; (The
Woodlands, TX) ; Zhang; Yibing; (Annandale,
NJ) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Kulkarni; Mohan G.
Zhang; Yibing |
The Woodlands
Annandale |
TX
NJ |
US
US |
|
|
Assignee: |
ExxonMobil Research and Engineering
Company
Annandale
NJ
|
Family ID: |
51619485 |
Appl. No.: |
14/226978 |
Filed: |
March 27, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61806076 |
Mar 28, 2013 |
|
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|
61806107 |
Mar 28, 2013 |
|
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61806115 |
Mar 28, 2013 |
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61919870 |
Dec 23, 2013 |
|
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61919949 |
Dec 23, 2013 |
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Current U.S.
Class: |
73/40.5R |
Current CPC
Class: |
G01M 3/002 20130101;
G01M 3/38 20130101; G01M 3/165 20130101 |
Class at
Publication: |
73/40.5R |
International
Class: |
G01M 3/04 20060101
G01M003/04 |
Claims
1. A method for detecting a leak in a pipeline, comprising:
providing along a length of a perimeter of a wall of a pipeline a
sensing cable including an optical fiber sensor array aligned with
a heating element; propagating at least one heat pulse through the
heating element along at least a portion of the sensing cable to
affect an exchange of thermal energy between the heating element
and fluid exposed to the sensing cable; measuring, over time, a
temperature profile of the sensing cable corresponding to the heat
pulse at each of a plurality of sensor locations on the optical
fiber sensor array; and detecting a leak in a pipeline by
determining one or more properties of the fluid exposed to the
sensing cable at each of the plurality of sensor locations based on
the temperature profile corresponding thereto.
2. The method of claim 1, wherein the sensing cable is provided
along an axial length of the perimeter of the wall of the
pipeline.
3. The method of claim 1, wherein the sensing cable further
includes an outer diameter including a polymer sheath.
4. The method of claim 1, wherein the sensing cable further
includes a power cable for optical signal amplification.
5. The method of claim 1, wherein the sensing cable includes one or
more steel armouring wires.
6. The method of claim 4, wherein the heating element comprises at
least one of the one or more steel armouring wires.
7. The method of claim 6, wherein the heating element includes a
resistive heating element and wherein propagating the at least one
heat pulse includes applying an electrical pulse with a
predetermined frequency and predetermined waveform.
8. The method of claim 6, wherein the heating element includes a
copper heating wire.
9. The method of claim 6, wherein propagating at least one heat
pulse through the heating element includes propagating the at least
one heat pulse through a heating element aligned adjacent to the
optical fiber sensor array.
10. The method of claim 6, wherein propagating at least one heat
pulse through the heating element includes propagating the at least
one heat pulse through a heating element disposed concentrically
with the optical fiber sensor array.
11. The method of claim 1, wherein measuring, over time, the
temperature profile includes measuring using fiber Bragg grating
array based sensing, Raman scattering based sensing, Rayleigh
scattering based sensing, or Brillioun scattering based
sensing.
12. The method of claim 1, wherein detecting the leak in the
pipeline includes comparing a difference in the one or more
properties of fluid exposed to the sensing cable between adjacent
sensor locations, and wherein the difference indicates a leak
between adjacent sensor locations if the difference exceeds a
predetermined threshold.
13. The method of claim 1, wherein determining the one or more
properties of the fluid exposed to the sensing cable at each of the
plurality of sensor locations includes comparing the temperature
profile at each of the plurality of sensor locations to one or more
predetermined temperature profiles, wherein each predetermined
temperature profile relates to a fluid with one or more
predetermined properties.
14. The method of claim 13, wherein at least a first predetermined
property relates to a fluid within the pipeline, and wherein
detecting the leak in the pipeline includes identifying, at one or
more of the plurality of sensor locations, a temperature profile
corresponding to the first predetermined property.
15. The method of claim 13, wherein at least a second predetermined
property relates to flow rate, and wherein detecting the leak in
the pipeline includes identifying, at one or more of the plurality
of sensor locations, a temperature profile corresponding to the
second predetermined property.
16. A system for detecting a leak in a pipeline, comprising: a
sensing cable including an optical fiber sensor array aligned with
a heating element disposed along a length of a perimeter of a wall
of a pipeline, the optical fiber sensor array having a plurality of
sensor locations; an excitation source coupled with the heating
element and configured to propagate at least one heat pulse through
the heating element along at least a portion of the sensing cable
to affect an exchange of thermal energy between the heating element
and fluid exposed to the sensing cable; an optical signal
interrogator coupled with the optical fiber sensor array and
adapted to receive a signal from each of the plurality of sensor
locations and configured to measure, over time, a temperature
profile of the sensing cable corresponding to the heat pulse at
each of the plurality of sensor locations on the optical fiber
sensor array; and a control unit, coupled with the heating element
and the optical signal interrogator, to detect a leak in the
pipeline by determining one or more properties of the fluid exposed
to the sensing cable at each of the plurality of sensor locations
based on the temperature profile corresponding thereto.
17. The system of claim 16, wherein the sensing cable is disposed
along an axial length of the perimeter of the wall of the
pipeline.
18. The system of claim 16, wherein the sensing cable further
includes an outer diameter including a polymer sheath.
19. The system of claim 16, wherein the sensing cable further
includes a power cable for optical signal amplification.
20. The system of claim 16, wherein the sensing cable includes one
or more steel armouring wires.
21. The system of claim 20, wherein the heating element comprises
at least one of the one or more steel armouring wires.
22. The system of claim 21, wherein the heating element includes a
resistive heating element and wherein the excitation source is
configured to propagate an electrical pulse with a predetermined
frequency and predetermined waveform, the electrical pulse
corresponding to the at least one heat pulse.
23. The system of claim 22, wherein the heating element includes a
copper heating wire.
24. The system of claim 21, wherein the heating element is aligned
adjacent to the optical fiber sensor array.
25. The system of claim 21, wherein the heating element is disposed
concentrically with the optical fiber sensor array.
26. The system of claim 16, wherein the optical fiber sensor array
and the optical signal interrogator include a fiber Bragg grating
array based sensing system, a Raman scattering based sensing
system, a Rayleigh scattering based sensing system, or a Brillioun
scattering based sensing system.
27. The system of claim 16, wherein the control unit is configured
to detect the leak in the pipeline by comparing a difference in the
one or more properties of fluid exposed to the sensing cable
between adjacent sensor locations, and wherein the difference
indicates a leak between adjacent sensor locations if the
difference exceeds a predetermined threshold.
28. The system of claim 16, wherein the control unit is configured
to determine the one or more properties of the fluid exposed to the
sensing cable at each of the plurality of sensor locations by
comparing the temperature profile at each of the plurality of
sensor locations to one or more predetermined temperature profiles,
wherein each predetermined temperature profile relates to a fluid
with one or more predetermined properties.
29. The system of claim 28, wherein at least a first predetermined
property relates to a fluid within the pipeline, and wherein the
control unit is configured to detect the leak in the pipeline by
identifying, at one or more of the plurality of sensor locations, a
temperature profile corresponding to the first predetermined
property.
30. The system of claim 28, wherein at least a second predetermined
property relates to flow rate, and wherein the control unit is
configured to detect the leak in the pipeline by identifying, at
one or more of the plurality of sensor locations, a temperature
profile corresponding to the second predetermined property.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Application Ser. Nos. 61/806,076, filed on Mar. 28, 2013,
61/806,107, filed on Mar. 28, 2013, 61/806,115, filed on Mar. 28,
2013, 61/919,870, filed on Dec. 3, 2013 and 61/919,949 filed on
Dec. 3, 2013, each of which is incorporated by reference in its
entirety herein, and from which priority is claimed.
BACKGROUND
[0002] 1. Field
[0003] The presently disclosed subject matter relates to methods
and systems for detecting a leak in a pipeline. More particularly,
the presently disclosed subject matter relates to detecting a leak
in a pipeline using a sensing cable including an optical fiber
sensor array aligned with a heating element.
[0004] 2. Description of Related Art
[0005] Components of certain equipment, such as that used in the
petroleum and petrochemical industry, which includes the
exploration, production, refining, manufacture, supply, transport,
formulation or blending of petroleum, petrochemicals, or the direct
compounds thereof, are often monitored to maintain reliable
operation. However, such components can involve harsh conditions,
such as high temperature, high pressure, and/or a corrosive
environment, making it difficult or costly to obtain reliable
measurements.
[0006] Energy and petroleum industry often requires use of
pipelines located in underwater environments. There is a continued
need to ensure such pipelines are free of significant leaks. For
example, detecting leaks in a pipeline can increase efficiencies,
and prevent or remediate spills and other undesirable
conditions.
[0007] Conventional techniques for pipeline leak detection include
computational pipeline monitoring (CPM), acoustic sensors,
distributed fiber optic temperature or acoustic sensors. CPM is a
wide-ranging term used to describe many computer-based leak
detection systems. It uses pipeline flow and/or pressure
measurements, governing models and alarm evaluation for leak
detection and confirmation. The governing models can be based on
mass balance, volume balance, pressure measurements, transient
fluid flow models, and/or statistical analysis of historical
pipeline events. CPM is the most commonly utilized and mature
technology for pipeline leak detection and has been used in both
onshore and offshore applications and the governing models have
been tested extensively. The main limitations of CPM include lower
sensitivity due to instrumentation performance and false positive
alarms in transient pipeline conditions. Other pipeline leak
detection techniques that are mainly used for pipeline leak
location involve acoustic sensors. Acoustic leak detection involves
sensing the pressure wave or sound generated by a leak. This is an
external type of system and is typically used for periodic
inspection or determining leak location after a leak alarm has been
generated by a method such as CPM. These sensors can be hand held
or mounted on a vehicle. The pressure difference created by the
leak is the most important parameter in detection. The
instrumentation signals are filtered using advanced signal
processing software. The signal is characteristic of leak flow
rate, pressure drop, type of fluid. Other relatively new leak
detection techniques involve the use of distributed fiber optic
sensors. This is external type of leak detection system. Pulses of
laser light are sent into a FO cable laid along the length of the
pipeline. The light is partially backscattered by the cable
material throughout the cable length generating scattered
components. This backscattering process is influenced by the cable
physical properties, which are in turn dependent on the ambient
temperature changes and acoustic vibrations that may be caused by
pipeline leaks. Therefore, by analyzing the characteristics of the
backscattered light, information, i.e. ambient temperature or
acoustic vibrations, associated with the pipeline leaks along the
cable may be obtained. The sensitivity of commercially available
fiber optic temperature or acoustic sensor cables needs to be
verified for pipeline leak detection.
[0008] However, there is a continued need for improved techniques
for detecting leaks in a pipeline.
SUMMARY OF THE INVENTION
[0009] The purpose and advantages of the disclosed subject matter
will be set forth in and apparent from the description that
follows, as well as will be learned by practice of the disclosed
subject matter. Additional advantages of the disclosed subject
matter will be realized and attained by the methods and systems
particularly pointed out in the written description and claims
hereof, as well as from the appended drawings. To achieve these and
other advantages and in accordance with the purpose of the
disclosed subject matter, as embodied and broadly described, the
disclosed subject matter includes systems and methods for detecting
a leak in a pipeline.
[0010] In accordance with one aspect of the disclosed subject
matter, a method for detecting a leak in a pipeline includes
providing along a length of a perimeter of a wall of a pipeline a
sensing cable including an optical fiber sensor array aligned with
a heating element. The method includes propagating at least one
heat pulse through the heating element along at least a portion of
the sensing cable to affect an exchange of thermal energy between
the heating element and fluid exposed to the sensing cable. The
method includes measuring, over time, a temperature profile of the
sensing cable corresponding to the heat pulse at each of a
plurality of sensor locations on the optical fiber sensor array.
The method includes detecting a leak in a pipeline by determining
one or more properties of the fluid exposed to the sensing cable at
each of the plurality of sensor locations based on the temperature
profile corresponding thereto.
[0011] As embodied herein, the sensing cable can be provided along
an axial length of the perimeter of the wall of the pipeline. The
sensing cable can include an outer diameter including a polymer
sheath. The sensing cable can include a power cable for optical
signal amplification. The sensing cable can further include one or
more steel armoring wires. The heating element can include a
resistive heating element, and propagating the at least one heat
pulse can include applying an electrical pulse with a predetermined
frequency and predetermined waveform. The heating element can
comprise at least one of the one or more steel armoring wires.
Additionally or alternatively, the heating element can include a
copper heating wire. The at least one heat pulse can be propagated
through a heating element aligned adjacent to the optical fiber
sensor array. Additionally or alternatively, the at least one heat
pulse can be propagated through a heating element disposed
concentrically with the optical fiber sensor array. Measuring the
temperature profile can include measuring using fiber Bragg grating
array based sensing, Raman scattering based sensing, Rayleigh
scattering based sensing, or Brillioun scattering based
sensing.
[0012] Furthermore, detecting the leak in the pipeline can include
comparing a difference in the one or more properties of fluid
exposed to the sensing cable between adjacent sensor locations, and
the difference can indicate a leak between adjacent sensor
locations if the difference exceeds a predetermined threshold.
Additionally or alternatively, determining the one or more
properties of the fluid exposed to the sensing cable at each of the
plurality of sensor locations can include comparing the temperature
profile at each of the plurality of sensor locations to one or more
predetermined temperature profiles, and each predetermined
temperature profile can relate to a fluid with one or more
predetermined properties. At least a first predetermined property
can relate to a fluid within the pipeline, and detecting the leak
in the pipeline can include identifying, at one or more of the
plurality of sensor locations, a temperature profile corresponding
to the first predetermined property. Additionally or alternatively,
at least a second predetermined property can relate to flow rate,
and detecting the leak in the pipeline can include identifying, at
one or more of the plurality of sensor locations, a temperature
profile corresponding to the second predetermined property.
[0013] In accordance with another aspect of the disclosed subject
matter a system for detecting a leak in a pipeline includes a
sensing cable including an optical fiber sensor array aligned with
a heating element disposed along a length of a perimeter of a wall
of a pipeline, the optical fiber sensor array having a plurality of
sensor locations. The system includes an excitation source coupled
with the heating element and configured to propagate at least one
heat pulse through the heating element along at least a portion of
the sensing cable to affect an exchange of thermal energy between
the heating element and fluid exposed to the sensing cable. The
system includes an optical signal interrogator coupled with the
optical fiber sensor array and adapted to receive a signal from
each of the plurality of sensor locations and configured to
measure, over time, a temperature profile of the sensing cable
corresponding to the heat pulse at each of the plurality of sensor
locations on the optical fiber sensor array. The system includes a
control unit, coupled with the heating element and the optical
signal interrogator, to detect a leak in the pipeline by
determining one or more properties of the fluid exposed to the
sensing cable at each of the plurality of sensor locations based on
the temperature profile corresponding thereto.
[0014] As embodied herein, the sensing cable can be disposed along
an axial length of the perimeter of the wall of the pipeline. The
sensing cable can include an outer diameter including a polymer
sheath. The sensing cable can include a power cable for optical
signal amplification. The sensing cable can further include one or
more steel armoring wires. The heating element can include a
resistive heating element, and the excitation source can be
configured to propagate an electrical pulse with a predetermined
frequency and predetermined waveform, the electrical pulse
corresponding to the at least one heat pulse. The heating element
can comprise at least one of the one or more steel armoring wires.
Additionally or alternatively, the heating element can include a
copper heating wire. The heating element can be aligned adjacent to
the optical fiber sensor array. Additionally or alternatively, the
heating element can be disposed concentrically with the optical
fiber sensor array. The optical fiber sensor array and the optical
signal interrogator can include a fiber Bragg grating array based
sensing system, a Raman scattering based sensing system, a Rayleigh
scattering based sensing system, or a Brillioun scattering based
sensing system.
[0015] In certain embodiments, the control unit can be configured
to detect the leak in the pipeline by comparing a difference in the
one or more properties of fluid exposed to the sensing cable
between adjacent sensor locations, and the difference can indicate
a leak between adjacent sensor locations if the difference exceeds
a predetermined threshold. Additionally or alternatively, the
control unit can be configured to determine the one or more
properties of the fluid exposed to the sensing cable at each of the
plurality of sensor locations by comparing the temperature profile
at each of the plurality of sensor locations to one or more
predetermined temperature profiles, and each predetermined
temperature profile can relate to a fluid with one or more
predetermined properties. At least a first predetermined property
can relate to a fluid within the pipeline, and the control unit can
be configured to detect the leak in the pipeline by identifying, at
one or more of the plurality of sensor locations, a temperature
profile corresponding to the first predetermined property.
Additionally or alternatively, at least a second predetermined
property can relate to flow rate, and the control unit can be
configured to detect the leak in the pipeline by identifying, at
one or more of the plurality of sensor locations, a temperature
profile corresponding to the second predetermined property.
[0016] It is to be understood that both the foregoing general
description and the following detailed description are exemplary
and are intended to provide further explanation of the disclosed
subject matter claimed.
[0017] The accompanying drawings, which are incorporated in and
constitute part of this specification, are included to illustrate
and provide a further understanding of the disclosed subject
matter. Together with the description, the drawings serve to
explain the principles of the disclosed subject matter.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1A is a schematic diagram of an exemplary sensing
system in accordance with the disclosed subject matter.
[0019] FIG. 1B is a cross sectional view of an exemplary sensing
cable configuration in accordance with the disclosed subject
matter.
[0020] FIG. 1C is a cross sectional view of another exemplary
sensing cable configuration in accordance with the disclosed
subject matter.
[0021] FIG. 2 depicts a representative plot of current and heat
pulses and corresponding temperature response in accordance with
the disclosed subject matter.
[0022] FIG. 3 is a graph illustrating a direct temperature sensing
technique for a plurality of sensor locations in accordance with
the disclosed subject matter.
[0023] FIG. 4A is a graph illustrating log-time regression sensing
technique in accordance with the disclosed subject matter.
[0024] FIG. 4B is a graph illustrating log-time regression sensing
technique for a plurality of sensor locations in accordance with
the disclosed subject matter.
[0025] FIG. 5A is a graph illustrating thermal excitation energy
concentration at harmonics and fundamental frequencies of heat
pulses in connection with a frequency spectrum sensing
technique.
[0026] FIG. 5B is a graph illustrating the phase of a
frequency-derivative spectrum in connection with frequency spectrum
sensing techniques over a plurality of sensor locations in
accordance with the disclosed subject matter.
[0027] FIG. 5C is a graph illustrating the amplitude of a
frequency-derivative spectrum in connection with frequency spectrum
sensing techniques over a plurality of sensor locations in
accordance with the disclosed subject matter.
[0028] FIG. 6 is a schematic representation of a system for
determining flow distribution through a component in accordance
with an exemplary embodiment of the disclosed subject matter.
[0029] FIG. 7 is an image and graph illustrating an exemplary
system and method for determining flow distribution through a
component in accordance with the disclosed subject matter.
[0030] FIG. 8 is a schematic representation of a plurality of
sensing cables arranged in grid patterns in accordance with an
exemplary embodiment of the disclosed subject matter.
[0031] FIG. 9 is a schematic representation of a system and method
for detecting a leak in a pipeline in accordance with the disclosed
subject matter.
[0032] FIG. 10A is a cross sectional view of an exemplary sensing
cable capable of detecting a leak in a pipeline in accordance with
the disclosed subject matter.
[0033] FIG. 10B depicts a cross sectional view of an alternative
exemplary sensing cables for detecting a leak in a pipeline in
accordance with the disclosed subject matter.
[0034] FIG. 11 illustrates exemplary principles of a system and
method for detecting a leak in a pipeline in accordance with the
disclosed subject matter.
[0035] FIG. 12 is a schematic representation of a system and method
for detecting a leak in a pipeline in accordance with the disclosed
subject matter.
DETAILED DESCRIPTION
[0036] As noted above and in accordance with one aspect of the
disclosed subject matter, methods disclosed herein include
detecting a leak in a pipeline. The method includes providing along
a length of a perimeter of a wall of a pipeline a sensing cable
including an optical fiber sensor array aligned with a heating
element. At least one heat pulse is propagated through the heating
element along at least a portion of the sensing cable to affect an
exchange of thermal energy between the heating element and fluid
exposed to the sensing cable. A temperature profile of the sensing
cable corresponding to the heat pulse at each of a plurality of
sensor locations on the optical fiber sensor array is measured,
over time. A leak in a pipeline is detected by determining one or
more properties of the fluid exposed to the sensing cable at each
of the plurality of sensor locations based on the temperature
profile corresponding thereto.
[0037] Furthermore, systems for detecting a leak in a pipeline are
also provided. Such systems include a sensing cable including an
optical fiber sensor array aligned with a heating element disposed
along a length of a perimeter of a wall of a pipeline, the optical
fiber sensor array having a plurality of sensor locations. An
excitation source coupled with the heating element is configured to
propagate at least one heat pulse through the heating element along
at least a portion of the sensing cable to affect an exchange of
thermal energy between the heating element and fluid exposed to the
sensing cable. The system includes an optical signal interrogator
coupled with the optical fiber sensor array and adapted to receive
a signal from each of the plurality of sensor locations and
configured to measure, over time, a temperature profile of the
sensing cable corresponding to the heat pulse at each of the
plurality of sensor locations on the optical fiber sensor array.
The system also includes a control unit, coupled with the heating
element and the optical signal interrogator, to detect a leak in
the pipeline by determining one or more properties of the fluid
exposed to the sensing cable at each of the plurality of sensor
locations based on the temperature profile corresponding
thereto.
[0038] Reference will now be made in detail to the various
exemplary embodiments of the disclosed subject matter, exemplary
embodiments of which are illustrated in the accompanying drawings.
The accompanying figures, where like reference numerals refer to
identical or functionally similar elements, serve to further
illustrate various embodiments and to explain various principles
and advantages all in accordance with the disclosed subject matter.
The accompanying figures, where like reference numerals refer to
identical or functionally similar elements, serve to further
illustrate various embodiments and to explain various principles
and advantages all in accordance with the disclosed subject matter.
For purpose of explanation and illustration, and not limitation,
exemplary embodiments of the disclosed subject matter are shown in
FIGS. 1-12.
[0039] In accordance with the disclosed subject matter,
characteristics of one or more materials can be measured with the
use of an optical fiber sensor array. The optical fiber can include
a plurality of discrete sensor locations provided along its length,
or the optical fiber itself can act as a plurality of sensor
locations aligned with a heating/cooling element in a sensing
cable. At least one heating/cooling pulse is propagated through the
heating/cooling element along at least a portion of the sensing
cable to affect an exchange of thermal energy between the
heating/cooling element and one or more media exposed to the
sensing cable. A temperature profile of the sensing cable (e.g., in
the time domain and/or spatial domain) corresponding to the
heating/cooling pulse at the plurality of sensor locations on the
optical fiber sensor array can be measured to support a variety of
techniques in accordance with the disclosed subject matter.
[0040] Generally, for purpose of illustration and not limitation,
thermal properties, such as material density, thermal conductivity,
heat capacity, or heat diffusion coefficient, of one or more
materials can be measured by generating a heat disturbance and
sensing a temperature response. In like fashion, dynamic physical
properties, such as the flow of a material, can also be measured.
As disclosed herein, techniques for measuring temperature can
include obtaining temperature measurements in both the temporal and
spatial domain. For example, distributed temperature sensing (DTS)
systems can provide temperature measurements along the length of a
sensing cable continuously or at regular intervals. The change in
these temperature measurements can correspond to certain properties
of a surrounding material or materials.
[0041] For purpose of illustration, and not limitation, an
exemplary system for measuring the characteristics of a material in
accordance with certain embodiments of the disclosed subject matter
will be described. In general, with reference to FIG. 1A, an
exemplary sensing system in accordance with the disclosed subject
matter can include a sensing cable 101 having disposed therein a
heating/cooling device 103 and optical fiber sensor array having a
plurality of sensors 102. The sensing cable 101 can be operatively
coupled with a control unit 106. For example, the heating/cooling
device 103 can be coupled with an excitation source 105, which in
turn can be coupled with the control unit 106. Likewise, the
optical fiber sensor array 102 can be coupled with a signal
interrogator 104, which can be coupled with the control unit 106.
Generally, uniform heat can be delivered (e.g., heat energy can be
provided or absorbed) along the sensing cable 101 via the
heating/cooling device 103 and the excitation source 105. A
temperature profile or its variation with time (e.g., variation
rate) can be measured using the optical fiber sensor array 102 and
signal interrogator 104. The control unit 106 can be adapted to
collect data, process data, and/or present data for visualization,
for example via one or more displays (not shown).
[0042] The sensing cable 101 can be arranged in a variety of
configurations. Two exemplary configurations are depicted in FIG.
1B and FIG. 1C, respectively. For example, FIG. 1B depicts a cross
section of a sensing cable 101 with the heating/cooling device 103
and the optical fiber sensor array 102 arranged in parallel with
each other. The sensing cable 101 can include, for example, an
outer casing (not shown) optionally filled with a filler material
110 to maintain the heating/cooling device 103 and optical fiber
sensor array 102 in place. Additionally or alternatively, the
filler can be extended about the heating/cooling device 103 and
temperature sensor 102 with or without the outer casing. The filler
can be, for example, a material with high thermal conductivity,
such as magnesium oxide (MgO). The outer casing can be a rigid
and/or durable material, for example a metal tube. To ensure
measurement accuracy, e.g., under harsh conditions, such as fouling
or corrosion, the sensing cable 101 casing can be treated with a
suitable coating, as described in more detail below. Alternatively,
and as depicted in cross section in FIG. 1C, the heating/cooling
device 103 and the temperature sensor array 102 can be generally
coaxial with each other, wherein the heating/cooling device 103 is
disposed concentrically around the temperature sensor array
102.
[0043] As embodied herein, the sensing cable 101 can be mineral
insulated for protection of a optical fiber sensor array 102
including one or more optical fibers. The optical fibers can be
coated and placed into a protective tube structure for enhanced
mechanical integrity and resistance to adversary effects of
environmental factors, such as H.sub.2, H.sub.2S and moisture. The
sensing cable 101 can further be protected using metal and mineral
insulation material (e.g., MgO) for effective thermal conduction.
The optical fibers can have a relatively small diameter, and thus
can be placed into a protective tube with a relatively small
diameter, allowing a faster thermal response and dynamic process
monitoring. One of ordinary skill in the art will appreciate that
the dimensions of the sensing cable 101 can be selected for a
desired application. For example, if further protection from the
local environment is desired, a sensing cable 101 with a larger
diameter, and thus additional filler, can be selected.
[0044] Furthermore, a number of commercially available fibers for
the temperature sensor 102 can be used, such as a Fiber Bragg
Grating array, Raman scattering based sensor, Rayleigh scattering
based sensor or Brillioun scattering based sensor. One of ordinary
skill in the art will appreciate that each type of fiber sensor can
have certain properties, such as response time, sensing resolution,
immunity to hydrogen darkening, effective sensing cable length, and
ability to sense temperature and/or strain, as illustrated for
purpose of example and not limitation in Table 1. For example, a
Fiber Bragg grating sensing system can include a relatively fast
response time, high spatial resolution, and can be employed over a
sensing cable length upwards of 100 km or longer in connection with
the use of optical fiber amplifiers. Raman and Brillioun scattering
sensing systems can have relatively low response times (e.g., on
the order of several seconds), and spatial resolution on the order
of centimeters. Rayleigh scattering sensing systems, when operated
to sense temperature, can have a response time of several seconds
with relatively high spatial resolution.
TABLE-US-00001 TABLE 1 Fastest Typical Immunity response point
sensor to H2 Longest sensor Sensor types time size (m) darkening
cable length Fiber Bragg <10 ms 0.01 high <100 km or Grating
(FBG) longer Raman >Several 0.25~0.5 low <100 km scattering
sensor seconds Rayleigh >Several 0.01 low <70 m scattering
sensor seconds (Temp) Rayleigh <1 ms 0.5 low <100 km
scattering sensor (Acoustic) Brillouin >Several 0.1~50 low
<100 km scattering sensor seconds
[0045] One of ordinary skill in the art will also appreciate that
certain of the various types of sensing systems can be used to
sense temperature and/or strain (e.g., to sense acoustics). For
example, Fiber Bragg Grating sensing systems can be used to measure
both temperature and strain, for purposes of sensing temperature
and acoustics. Raman scattering sensing systems are typically used
to sense temperature. Brillioun scattering sensing systems can be
used to measure temperature and strain, and are typically used to
sense temperature. Rayleigh scattering sensing systems can be used
to measure temperature and strain, and can be used to sense either
temperature or acoustics. One of ordinary skill in the art will
appreciate that when Rayleigh scattering sensing systems are used
to sense acoustics, response time can increase to lower than 1 ms
and spatial resolution can increase to approximately 50 cm.
[0046] Referring again to FIG. 1A, and as noted above, the control
unit 106 can be coupled with the signal interrogator 104. The
signal interrogator 104 can be, for example, an optical signal
interrogator. Various optical signal interrogators may be used,
depending on the type of optical fiber sensing techniques to be
employed. The controller 106 can be adapted to perform signal
processing on real-time temperature data provided by the signal
interrogator 104. For example, the control unit 106 can be adapted
to identify and record continuous or repeated temperature
measurements at each of a plurality of sensor locations along the
sensing cable 101. Additionally, the control unit 106 can be
adapted to process temperature measurements over time to identify a
characteristic of the material surrounding the sensing cable at one
or more sensor locations.
[0047] As disclosed herein, a variety of suitable methods can be
employed for generating the heating/cooling pulse along the sensing
cable 101. As used herein, the term "pulse" includes a waveform of
suitable shape, duration, periodicity, and/or phase for the
intended purpose. For example, and not limitation, and as described
further below, the pulse may have a greater duration for one
intended use, such as the determination of deposits, and a shorter
duration for another intended use, such as the determination of
flow. As embodied herein, the heating/cooling device 103 can be an
electrically actuated device. For example, the heating/cooling
device 103 can include a resistive heating wire, and the excitation
source 105 can be electrically coupled with the heating wire and
adapted to provide a current therethrough. Passing of a current
through the resistive heating wire can provide thermal energy along
the length of the sensing cable 101, thereby generating a uniform
heating/cooling effect along the sensing cable. Alternatively, the
heating/cooling device 103 can include a thermoelectric device, and
can be likewise coupled to the excitation source 105. The
thermoelectric device can use the Peltier effect to heat or cool a
surrounding medium. That is, for example, the thermoelectric device
can be a solid-state heat pump that transfers heat from one side of
the device to the other. The thermoelectric device can be
configured, for example, to provide heating to the optical fiber
sensor for a certain polarity of electric potential and cooling for
the opposite polarity. As disclosed herein, and for purpose of
simplicity, the terms "heating/cooling device", and
"heating/cooling pulse" will be referred to generally as a "heating
device" or "heating element" and as a "heat pulse," respectively.
Depending upon the context, such terms are therefore understood to
provide heating, cooling, or both heating and cooling.
[0048] In certain embodiments of the disclosed subject matter, the
excitation source 105 can be configured to deliver current in a
predetermined manner. For example, the excitation source 105 can be
configured to generate pulses having predetermined wave forms, such
as square waves, sinusoidal waves, or saw tooth waves. The
excitation source 105 can be configured to generate the pulses at a
predetermined frequency. For example, and not limitation, and with
reference to FIG. 2, the excitation source 105 can be configured to
generate an electric pulse of a rectangular wave form 210 through
the heating/cooling element 103. The electric pulse can create a
heat pulse 220 in the heating/cooling element 103 with the same
wave form. That is, for example, the heat flow through the
heating/cooling element 103 can be given by I.sup.2R/A, where I is
the current, R is the resistance of the heating/cooling element
103, and A is the surface area of a cross section of the
heating/cooling element 103. The heat pulse can result in a heat
exchange between the sensing cable 101 and the surrounding media.
The temperature at each sensor location can be recorded to generate
a "temperature profile" 230 for each sensor location. For example,
the temperature at each sensor location can be recorded with a
sampling frequency of 50 Hz. The temperature profile 230 can
correspond to characteristics of the medium surrounding the sensing
cable 101 at each sensor location.
[0049] For purposes of illustration, and not limitation, the
underlying principles of thermally activated ("TA") measurement
techniques will be described generally. Prior to heating or cooling
by the heating/cooling device 103, temperature measurements of the
surrounding medium can be taken with the optical fiber sensor array
102 of the sensing cable 101 and the temperature profile can be
recorded as a reference. Due to the Joule effect, the heating
device 103 can deliver a constant and uniform heat along the cable,
heating up both cable and surrounding medium near the cable
surface. For purposes of illustration, the temperature measured by
the optical fiber can be described by the following equation:
.differential. T .differential. t = 1 mc p ( E . gen - E . loss ) ,
( 1 ) ##EQU00001##
where .sub.gen is the heat generation rate per unit length from the
heating device, .sub.loss is the heat loss rate due to heat
transfer from the sensing cable to the surrounding medium, and m
and c.sub.p represent the mass and heat capacitance of the sensing
cable per unit length. The heat generation within the sensing cable
due to the Joule effect can be given by:
.sub.gen.varies.Zi.sup.2, (2)
where Z is the impedance of the sensing cable per unit length and
the rate of heat loss from the sensing cable to the surrounding
media can be decomposed into heat diffusion and heat convection
(e.g., .sub.loss can include both heat diffusion (conduction) in a
stationary medium and or convective heat transfer in a flowing
medium):
.sub.loss= .sub.diffusion+ .sub.convection (3)
For a stationary medium, the heat loss term can be given as:
.sub.loss.varies.Ak.DELTA.T, (4)
where A is effective heat transfer area of the sensing cable, k is
effective heat conduction coefficient of the medium and .DELTA.T is
the effective temperature gradient across the sensing cable and the
medium.
[0050] The heat capacitance of the cable per unit length can limit
the frequency of the thermal response of the cable, and thus the
cable can be designed with a heat capacitance suited to the desired
data frequency. Because heat generation can be relatively constant
and uniform, the rate of change in localized temperature can depend
primarily on the heat transfer between the cable and the
surrounding medium. If the localized heat transfer is high at a
particular point on the sensing cable, then the rate of change of
temperature at that point along the cable, measured by one
temperature sensor in the optical fiber, can be small. Otherwise,
the temperature changing rate will be large. When subject to a
heterogeneous medium or a mixed medium consisting of layers of
different fluids or the like, the spatial distribution of the
temperature along the sensor array can be indicative of the
interface between the different media.
[0051] For purpose of illustration, and not limitation, transient
temperature analysis techniques to determine characteristics of a
medium will now be described with the sensing cable modeled as an
infinitely long thin cylinder placed in an infinite homogeneous
medium. For purposes of this description, it is assumed that at
time zero (t=0) an electrical current, i, and the heat generation
rate per length of the cylinder is given by:
q=.pi.r.sub.0.sup.2z.sub.0i.sup.2, (5)
where r.sub.0 is the radius of the cylinder, and z.sub.0 is the
resistance of the cylinder per unit of volume. A closed form
solution for the temperature on the surface of the cylinder can be
given as:
T ( r 0 , t ) - T .infin. = q 4 .pi. k .intg. r 0 2 4 .alpha. t
.infin. - u u u , ( 6 ) ##EQU00002##
where k and .alpha. are the heat conductivity and diffusivity
coefficients of the medium, and T.sub..infin. is the initial
temperature distribution along the sensing cable. The normalized
temperature change and normalized time t can be defined as:
.DELTA. T * = T ( r 0 , t ) - T .infin. q / ( 4 .pi. k ) and ( 7 )
t * = 4 .alpha. t r 0 2 . ( 8 ) ##EQU00003##
Equation 6 can thus be given as:
.DELTA. T * = .intg. 1 / t * .infin. - u u u . ( 9 )
##EQU00004##
The incomplete gamma function can have following expansion form for
small but non-zero value of z (0<z<2.5)
.GAMMA. ( z ) = .intg. z .infin. - u u u = - .gamma. - ln ( z ) - n
= 1 .infin. ( - z ) n n ( n ! ) . ( 10 ) ##EQU00005##
The temperature response as given by equation 6 above can be
further approximated as
.DELTA.T*.apprxeq.-.gamma.-1n(1/t*), (11)
when
z=1/t*<<1. (12)
[0052] In accordance with this illustrative and non-limiting model,
comparison of the normalized temperature change as a function of
normalized time (e.g., as given by equation 9 and equation 11,
respectively) indicates that when the normalized time is greater
than approximately 10, equation 11 is a good approximation of
normalized temperature change. Moreover, equation 11 above
indicates that temperature change can increase linearly with the
log of time when the heating time is sufficiently large so as to
satisfy the criteria in equation 12. Thus, the equation can be
written as:
.DELTA.T(r.sub.0,t).apprxeq.a+b1n(t), 13)
where parameters a and b are function of thermal properties of the
medium for given heating rate, and are given by:
a = q 4 .pi. k ( - .gamma. - ln ( r 0 2 4 .alpha. ) ) and ( 14 ) b
= q 4 .pi. k . ( 15 ) ##EQU00006##
[0053] Thus, equation 13 can provide a theoretical basis for
determining the thermal properties of a medium based on measurement
of transient temperature. One of ordinary skill in the art will
appreciate that continuous heating can consume more electrical
energy and make measurements less sensitive to dynamic change of
the thermal properties to be measured (e.g., when the medium
mixture changes with time), and thus pulsed heating in accordance
with the disclosed subject matter can provide benefits such as
decreased electrical energy usage and for measurement of dynamic
conditions of surrounding materials.
[0054] For purpose of illustration, and not limitation, an
exemplary method of measuring the characteristics of the media
surrounding the sensing cable using thermal analysis sensing
techniques will be described. In general, an optimized waveform of
electrical pulse (for example, a square wave) can be delivered
along the length of the heating/cooling device 103, and temperature
can be monitored using a temperature sensor array 102, e.g.,
optical fiber sensors. Owing to the uniformity of the
heating/cooling effect along the sensing cable, temperature
readings can vary depending on localized heat transfer process,
which can be a function of the thermal properties (e.g., thermal
conductivity, heat capacity) and physical conditions (static or
flow) of the medium surrounding the sensing cable 101. The control
unit 106 can be adapted to determine the characteristics of the
surrounding media simultaneously, using the temperature
profile.
[0055] A single heating pulse (e.g., arising from an optimized
waveform of electrical pulse) can create a temperature response
which can be derived in accordance with the exemplary and
non-limiting model described herein using superposition as
follows:
T ( r 0 , t ) - T .infin. = q 4 .pi. k ( .intg. r 0 2 4 .alpha. t
.infin. - u u u - .intg. r 0 2 4 .alpha. ( t - t 0 ) .infin. - u u
u ) . ( 16 ) ##EQU00007##
The first term in the bracket of equation 16 can represent the
heating from t to t.sub.0, and the 2nd term the cooling after
t.sub.0. Data collected during heating and cooling are analyzed
separately, as disclosed herein, to derivate estimates of thermal
properties of the medium.
[0056] Based upon the above, the control unit 106 can be adapted to
determine the characteristics of the surrounding media using a
variety of suitable techniques. For example, the temperature
profile at each sensor location can be used to determine the
characteristics of the surrounding media directly. The temperature
measurements during heating and/or cooling of the sensing cable,
corresponding to the timing of the rectangular electrical pulse,
can be used to generate a feature-temperature profile at each
sensor location. For example, the feature-temperature profiles can
be extracted from the temperature data at distinctive conditions:
heating (e.g., the condition during which the heat pulse is passing
over a sensor location), cooling (e.g., the condition during which
the heat pulse has passed over the sensor location and heat is
being exchanged between the sensing cable and the surrounding
media) and peak temperature (e.g., approximately the maximum
temperature recorded at the sensor location for each heat
pulse).
[0057] For purpose of illustration, and not limitation, and with
reference to FIG. 3, the control unit 106 can be configured to
determine temperature characteristics of surrounding media using
the feature-temperature profile at each sensor location. FIG. 3
shows distribution of feature temperatures along a sensing cable
exposed to different media at different sensor locations. Graph 330
depicts the measured temperature profiles for a plurality of sensor
locations. In accordance with the disclosed subject matter,
feature-temperatures 331b, 332b, and 333b can be extracted from the
measured temperature profile depicted in graph 330. For example, at
each sensor location, feature-temperature 331b can correspond to a
heating condition (e.g., while the heat pulse is passing over the
sensor location), and can be extracted for each sensor location at
a corresponding time 331a. Likewise, feature-temperature 332b can
correspond to a peak temperature, and can be extracted for each
sensor location at a corresponding time 332a. Similarly, feature
temperature 333b can correspond to a cooling condition (e.g., after
the heat pulse has passed over the sensor location and during which
heat exchange between the cable and the surrounding media takes
place) and can be extracted for each sensor location at a
corresponding time 333a. Temperature 310 is the measured
temperature at each sensor location during ambient conditions
(e.g., no heat is applied).
[0058] As illustrated by FIG. 3, the feature temperature at each
sensor location can correspond to the temperature characteristics
of the surrounding media. For example, as depicted in FIG. 3, a 36
inch sensing cable arranged in a vertical configuration with a
sensor disposed or located each unit inch along the cable can be
exposed to a stack of air, oil, emulsion, and water. It should be
noted that FIG. 3 depicts data from 24 sensor locations. Assuming
each medium is stationary around the sensing cable, the rate of
heat exchange, and thus the feature-temperature profiles 331b,
332b, and 333b, between the sensing cable and the surrounding media
at each sensor location can correspond to the heat conduction of
the surrounding media. That is, for example, heat transfer between
the sensing cable and surrounding air can be lower than that
between the sensing cable and water, as water has a higher heat
conduction. Oil and emulsion layers can also be identified in this
manner.
[0059] The determination of the characteristics of the media
surrounding the sensing cable can be achieved by further
configuring the control unit 106 to process the temperature
profile. For example, in accordance with certain embodiments of the
disclosed subject matter, the regression of the temperature over
log of time can be performed over an interval of time corresponding
to each heat pulse for each sensor location. The slope and
intercept of the regression can be used to identify the material
characteristics. For example, the regression can take the
functional form of T=b+m1n(t), where T is the temperature
measurement, 1n(t) is the natural log of the time of the
temperature measurement, b is the intercept of the regression, and
m is the regression coefficient.
[0060] The interval over which the regression is taken can be, for
example, during the heating condition described above (e.g., during
which the heat pulse passes over the sensor location). Because
heating can occur in a logarithmic manner, taking the regression as
a function of the log of time and provide for results with lower
error (e.g., a higher correlation coefficient). That is, for
example, the temperature as a function of the log of time can be
substantially linear over the heating period. Alternatively, the
interval over which the regression is taken can be during the
cooling condition described above. For purpose of illustration, and
not limitation, for a square electrical pulse from 0 current to a
constant non-zero value, the constant non-zero current value can
correspond to the heating stage, and zero current can correspond to
the cooling stage. The slope of the regression for the heating
stage can be computed over a fraction of pulse duration when the
current is non-zero, while slope of the regression for the cooling
stage can be computed over a fraction of the time for which the
current changes to zero value. Additionally or alternatively, the
regression can take a number of suitable functional forms. For
example, an nth order polynomial regression can be taken if the
functional form of the temperature profile resembles an nth order
polynomial.
[0061] For purpose of illustration, FIG. 4A shows the regression
results of one temperature measurement at a sensor location in each
material of FIG. 3. Line 420 corresponds to a plot of temperature
at a sensor location in oil over the log of time. Likewise, lines
430, 440 and 450 correspond to a plot of temperature at a sensor
location in air, emulsion, and water, respectively, over the log of
time. Regression can be performed over a regression interval 410,
which can correspond to the heating condition of the respective
temperature sensor. The results of the regression can be plotted.
For example, line 421 is a plot of the regression of line 420. As
illustrated by FIG. 4A, the slope and intercept of each regression
can correspond to a characteristic of the surrounding material, and
such characteristics can be determined. That is, with reference to
FIG. 4A, each material having different thermal characteristics can
have a different slope and intercept, and can thus be identified.
As depicted in FIG. 4A. The deviations in measurements resulting
from the linear fitting line after the regression interval, as
shown by line 420 and line 421, can be due to boundary effects from
the wall of the vessel. One of ordinary skill in the art will
appreciate that the description of the underlying principles herein
assumes the thermal energy delivered by the sensing cable diffuses
out without any boundaries. However, in the presence of such
boundaries, thermal energy will be contained in a finite space and
eventually thermal equilibrium will be reached. Accordingly, the
regression interval can be selected based on a desired application,
including corresponding boundary conditions.
[0062] For purpose of illustration, FIG. 4B shows the regression
results for 24 temperature sensors of FIG. 3, showing both slopes
450 and intercepts 470. As illustrated by FIG. 4A and FIG. 4B, in
certain circumstances these techniques can provide determination of
material characteristics with reduced error, comparing results from
FIG. 4B with FIG. 3 to differentiate the emulsion layer and the oil
layer. The interval over which the regression can be performed can
be predetermined to reduce boundary effect errors (e.g., error 422
induced by boundary effects in the plot of line 420). That is, for
example, taking the regression over a small interval can omit
certain features of a temperature profile that can correspond to a
particular characteristic. Accordingly, the regression interval can
be predetermined such that errors induced by boundary effects are
reduced. For example, the regression interval can be predetermined
by calibration and/or with reference to known parameters or
operating conditions of the system, such as expected features of a
temperature profile.
[0063] In accordance with another aspect of the disclosed subject
matter, enhanced determination of the characteristics of media
surrounding the sensing cable can be achieved with a control unit
106 configured to process the temperature profile in the frequency
domain. A N-pulse train (i.e. application of a certain periodic
form of current through the sensing cable to generate N cycles of
heating and cooling) can be propagated through the heating/cooling
element 103. The period of a heating/cooling cycle, t.sub.0, the
number of heating cycles, N, and the current amplitude, I.sub.0,
can be selected. The heating/cooling pulses can be applied to the
heating/cooling element 103 with the excitation source 105 to
generate thermal excitation within the sensing cable 101.
[0064] Temperature readings from the optical fiber sensor array 102
can be collected via the signal interrogator 104 at a selected
sampling frequency. The sampling frequency can be, for example, at
least twice the maximum signal frequency of interest. A temperature
series, T.sub.i(1), T.sub.i(2), T.sub.i(3), . . . can be generated
where i=1, 2, 3, . . . M, is the sensor index. In accordance with
certain embodiments, synchronized sampling techniques can be
employed to reduce the sample number, increase the signal to noise
ratio, and improve Fourier transform accuracy. The time difference
of the temperature readings .DELTA.T=[T(k+1)-T(k)]/.DELTA.t, can be
calculated using the control unit 106 to generate time series of
temperature derivative .DELTA.T.sub.i(1), .DELTA.T.sub.i(2),
.DELTA.T.sub.i(3) . . . , where sensor index i=1, 2, 3 . . . M. In
connection with the following description, the temperature
difference, differenced temperature, or temperature derivatives are
all referred to as the time series .DELTA.T'. A transform (e.g., a
Fast Fourier Transform [FFT], or Discrete Fourier Transform [DFT])
can be applied, using the control unit 106, to generate a spectrum
of time series of temperature difference for M sensors. For each
sensor, the real and imaginary values of the spectrum at
fundamental frequency of N-Pulse train can be selected
f.sub.0=1/t.sub.0. The characteristics of the surrounding media can
thus be determined as disclosed herein using M pairs of the values
derived from the spectrum of the temperature difference as
described above. Alternatively, the frequency differenced spectrum
(i.e., obtained by applying the operation of taking the derivative
of the spectrum of temperature difference with respect to the
frequency) and the real and imaginary values of the differenced
spectrum can be used. The characteristics of the surrounding media
can thus be determined as disclosed herein using M pairs of the
values derived from the differenced spectrum as described
above.
[0065] That is, for example, the time derivative of the temperature
data can be determined (i.e., resulting in the differenced
temperature). The Fourier transform of the time-derivative
temperature can then be determined, and the derivative of the
complex spectrum with respect to the frequency can be calculated
(i.e., resulting in the differenced spectrum). The amplitude and
phase of the frequency-derivative spectrum (differenced spectrum)
can then be calculated. The amplitude and phase of the
frequency-derivative spectrum can correspond to the characteristics
of the surrounding media at each sensor location. For purpose of
illustration, FIG. 5B shows the phase of the frequency-derivative
spectrum of the temperature measurements over the sensor locations
as illustrated in FIG. 3. Likewise, FIG. 5C shows the amplitude of
the frequency-derivative spectrum of the temperature measurements
over the sensor locations as illustrated in FIG. 3. As illustrated
by the figures, the techniques disclosed herein can provide for
enhanced accuracy in the measurement and differentiation of the
levels and interfaces between the air, oil, emulsion, and water
layers.
[0066] As embodied herein, the sensing cable 101 can be calibrated,
e.g., with the control unit 106. Calibration can include
calibrating the sensor array to ensure that each sensor at a
different location along the sensing cable provides the same output
when subject to the same material of a constant thermal property.
For example, the sensing cable 101 can be submerged into a
homogenous medium of known thermal property, and the temperature
measurements and processing techniques disclosed herein can be
applied. If there is a difference between sensor output, the
difference can be used as compensation and can be applied during
measurements. Additionally, calibration can include ensuring that
the sensor output accurately estimates the particular
characteristic of interest (e.g., thermal conductivity and/or
diffusivity). For example, a number of materials with known thermal
properties can be measured for a broad range of values and a
database can be constructed including correlations between
measurements and determined characteristics of the known materials.
The database can then be used to interpolate a measured
characteristic of an unknown material.
[0067] For purpose of illustration, and not limitation, the
underlying theory of measurement techniques in accordance with this
exemplary embodiment will be described. In connection with this
description, for purpose of example, the waveform of the pulse
train propagated through the heating device can be a square shape
current, e.g., as illustrated in FIG. 2. The current can be defined
mathematically as:
i ( t ) = n = 1 N { H ( t - ( n - 1 ) t 0 ) - H ( t - ( n - 1 2 ) t
0 ) } I 0 , ( 17 ) ##EQU00008##
where t.sub.0 is the period, I.sub.0 is the amplitude of the
current, and H denotes the Heaviside step function defined by:
H ( x - x 0 ) = { 0 x < x 0 1 x .gtoreq. x 0 . ( 18 )
##EQU00009##
The heating rate can thus be given as:
q ( t ) = n = 1 N { H ( t - ( n - 1 ) t 0 ) - H ( t - ( n - 1 2 ) t
0 ) } q 0 , ( 19 ) ##EQU00010##
where q.sub.0 is related to the current by equation 5.
[0068] Instead of analyzing the temperature in time domain, the
temperature rate, i.e., the derivative of the temperature with
respect to time, can be considered in the frequency domain. The
derivative operation, a high-pass filtering, can remove the
slow-varying trend of the temperature for easier analysis. The time
derivative of the temperature and heating generation rate can be
defined as follows:
T . ( r , t ) = T t and ( 20 ) q . ( t ) = q t . ( 21 )
##EQU00011##
[0069] In frequency domain, the counterparts to the temperature and
heating generation rate can be complex spectrum functions of S(r,
.omega.) and .OMEGA.(.omega.). For large distances away from the
heating element, the thermal diffusion process can exhibit the
behavior of an attenuated and dispersive wave. The complex spectrum
of the change rate of the temperature on the sensing cable's
surface can be given as:
S ( r 0 , .omega. ) = 1 2 .pi. k .OMEGA. ( .omega. ) .kappa. r 0 H
0 ( 2 ) ( .kappa. r 0 ) H 1 ( 2 ) ( .kappa. r 0 ) . ( 22 )
##EQU00012##
The contribution of the heating component, .OMEGA. at a center
frequency of .omega., to the change rate of the temperature on the
sensing cable's surface can thus be given as:
d{dot over
(T)}(r.sub.0,.omega.,t)=S(r.sub.0,.omega.)e.sup.j.omega.td.omega..
(23)
[0070] Integration of above over all frequencies can recover the
temperature rate in time domain. Therefore, S can be used as
indicator of the medium. For purpose of illustration, and not
limitation, the excitation term, .OMEGA. will now be described in
greater detail. From equations 19 and 21, the derivative of the
heating generation can be given as:
q . ( t ) = i = 1 N { .delta. ( t - ( i - 1 ) t 0 ) - .delta. ( t -
( i - 1 2 ) t 0 ) } q 0 ( 24 ) ##EQU00013##
in time domain, and:
.OMEGA. ( .omega. ) = q 0 ( j.omega. t 0 - j .omega. t 0 2 ) n = 1
N j ( n .omega. t 0 ) ( 25 ) ##EQU00014##
in frequency domain. Because N is finite, .OMEGA. can contain all
frequencies. The components at the harmonic frequencies can be
given as:
.omega. k = k .omega. 0 = k 2 .pi. t 0 , ( 26 ) ##EQU00015##
with index k.
[0071] Evaluation of equation 25 at the harmonic frequencies
gives:
.OMEGA. ( .omega. ) = { 2 Nq 0 k = 1 , 3 , 5 0 k = 0 , 2 4 . ( 27 )
##EQU00016##
As such, .OMEGA. peaks at odd harmonics but zeros at even
harmonics. At non-harmonic frequencies, .OMEGA. is complex in
general. FIG. 5A depicts an exemplary plot of .OMEGA./q.sub.0 verse
.omega./.omega..sub.0 for N=1, 2, or 3. Accordingly, the thermal
excitation energy can be concentrated at odd harmonics of
fundamental frequency of pulses and increase as N increases.
[0072] As embodied herein, one of the odd harmonic frequencies can
be chosen to increase signal to noise ratio in analysis of
temperature measurements. In this manner, any temperature variation
introduced by non-electrical heating can introduce noise which
could be difficult to handle in time domain but can be reduced in
frequency domain via N-pulse train: the number of cycles, N, can be
increased to boost the peak value at odd harmonics. Additionally or
alternatively, synchronized sampling techniques or harmonic
tracking can also be used to reduce the noise.
[0073] In accordance with certain embodiments, the spectrum
S(.omega.), e.g., as given in equation 22, can be used to estimate
the thermal property of a medium surrounding the sensing cable. A
characteristic frequency can be given as:
.omega. * = .alpha. r 0 2 . ( 28 ) ##EQU00017##
The complex argument to the Hankel functions can thus become:
.kappa. r 0 = - j .omega. .alpha. r 0 = .omega. .omega. * j .theta.
, ( 29 ) ##EQU00018##
Where .theta.=3/4.pi. for .omega.>0. At low frequencies where
.omega./.omega.* (amplitude of .kappa.r.sub.0) is less than 1, the
Hankel functions can be approximated as:
H 0 ( 2 ) ( .kappa. r 0 ) .apprxeq. 1 - ( .kappa. r 0 ) 2 4 - j
.pi. 2 ln ( .kappa. r 0 ) and : ( 30 ) H 1 ( 2 ) ( .kappa. r 0 )
.apprxeq. .kappa. r 0 2 - ( .kappa. r 0 ) 3 16 + j 2 .pi. 1 .kappa.
r 0 . ( 31 ) ##EQU00019##
The spectrum, S, can thus reduce to:
S ( r 0 , .omega. ) = .OMEGA. 2 .pi. k X ^ ( .omega. .omega. * ) ,
( 32 ) ##EQU00020##
where the normalized transfer function, and temperature change
response to the thermal excitation .OMEGA./2.pi.k at frequency
.omega./.omega.* can be given as:
X ^ ( .omega. .omega. * ) = ( R s + j I s ) = X j .phi. , ( 33 ) R
s .apprxeq. 1 32 ( .omega. .omega. * ) 2 + 1 2 .pi. .omega. .omega.
* + 1 2 .pi. ( .omega. .omega. * - 4 .pi. ) ln ( .omega. .omega. *
) 1 4 ( .omega. .omega. * ) 2 - 2 .pi. ( .omega. .omega. * ) + 4
.pi. 2 , and ( 34 ) I s .apprxeq. 5 4 ( .omega. .omega. * - 4 .pi.
) - 1 16 .pi. ( .omega. .omega. * ) 2 ln ( .omega. .omega. * ) 1 4
( .omega. .omega. * ) 2 - 2 .pi. ( .omega. .omega. * ) + 4 .pi. 2 ,
( 35 ) ##EQU00021##
after neglecting terms of higher order.
[0074] As disclosed herein, and in accordance with certain
embodiments of the disclosed subject matter, the amplitude and
phase can decrease monotonically with frequency so that higher
frequency corresponds with lower response of temperature to the
heating. Accordingly, lower frequencies can obtain significant
heating response and higher signals. Additionally, the imaginary
part of the complex spectrum can be nearly linear with the
frequency while the real part can exhibit linear behavior beyond
certain frequency values. Therefore, the derivative of the transfer
function spectrum with respect to frequency can lead to constants
beyond certain values of .omega./.omega.*. One of ordinary skill in
the art will appreciate that, mathematically, the spectral
derivative is equivalent to the Fourier transform of the
temperature rate with respect to the log of time. Thus there is
connection of the derivative spectrum with the linear relationship
of the temperature change with log(t) in the time domain as shown
in equation 13.
[0075] As embodied herein, systems and methods in accordance with
another aspect of the disclosed subject matter can include
determining the liquid/gas flow distribution of a fluid through a
component with a sensing cable including an optical fiber sensor
array aligned with a heating/cooling element. The method can
include propagating at least one heating/cooling pulse through the
heating/cooling element along at least a portion of the sensing
cable to affect an exchange of thermal energy between the heating
element and the fluid exposed to the sensing cable. The method can
include measuring, over time, a temperature profile of the sensing
cable corresponding to the heat pulse at each of a plurality of
sensor locations on an optical fiber sensor array. The method can
include determining a flow distribution of the fluid by determining
one or more properties of the fluid exposed to the sensing cable at
each of the plurality of sensor locations based on the temperature
profile corresponding thereto.
[0076] For purpose of illustration and not limitation, reference is
made to the exemplary embodiments of FIG. 1. The method and system
disclosed herein can be used to determine flow distribution in
variety of components and vessels. For example, the component can
be a particulate bed, a wash bed including packing material, an
absorbent bed, a structured bed, a filter, or the like. In
operation, it can be desirable to determine flow conditions through
such components. For example, fixed bed reactors, such as
hydrotreating reactors and hydrocracking reactors, can develop
liquid/gas maldistribution and corresponding localized "hot spots,"
which can cause a runaway condition in exothermic reactions within
the reactor. As another example, liquid/gas maldistribution can
occur in components such as the wash beds of a vacuum pipe still
("VPS") distillation tower, which can cause problems such as
unplanned capacity loss, increased operational costs, and increased
energy usage. Determination of flow distribution of a fluid through
such components can allow for mitigation strategies, such as
increasing the flow rate of wash oil or otherwise varying
operational parameters of the component. Accordingly, the
techniques disclosed herein can be employed to determine the flow
distribution of a fluid through a component in connection with a
refining operation. However, it is recognized that the system and
method herein can be applied to numerous other environments and
vessels in which the determination of flow distribution is
beneficial.
[0077] In accordance with this exemplary embodiment, the system for
detecting a liquid/gas flow distribution vessel can include the
components and features described herein with reference to FIG.
1A-C. The sensing cable (e.g., sensing cable 101) can further
include an anti-fouling coating to resist fouling and/or coking
deposition on the sensing cable. For example, the sensing cable can
be coated with a suitable coating to resist coking, such as Teflon,
or coatings formed from modified fluoropolymer and co-polymer
reinforcements. These coatings can be engineered for high release
(non-stick), non-wetting, thermal stability, dielectric strength
and chemical resistance, where comparatively thin films are desired
or otherwise beneficial.
[0078] Using the systems and techniques as disclosed, and suitable
modifications as desired, a method of determining the flow
distribution of a fluid through a component is provided and
disclosed herein with reference to FIG. 1A through FIG. 5. For
purpose of example, and with reference to FIG. 6, the method of
determining the flow distribution of a fluid through a component
will be described in connection with certain exemplary embodiments,
wherein the vessel is a fixed bed, such as in a fixed bed of a
hydrotreating or hydrocracking reactor or a fixed structured wash
oil bed of a VPS distillation tower. One of ordinary skill in the
art will appreciate that the techniques disclosed herein can be
applied in connection with a variety of suitable components, and
the disclosed subject matter is not intended to be limited to the
exemplary embodiments disclosed herein.
[0079] With reference to FIG. 6, the method of flow through a
vessel 810 can include positioning a sensing cable 101 within a
wash bed 820 of a VPS distillation tower 810. For example, the
sensing cable 101 can be positioned across a surface of the wash
bed 820 such that the sensing cable 101 is aligned perpendicular to
an axis of the vessel 810. In this manner, sensor locations along
the sensing cable 101 can correspond to locations about a cross
section of the vessel 810. The sensing cable 101 likewise can be
positioned and/or arranged in a variety of other suitable
configurations as desired or needed. For example, the sensing cable
101 can be positioned parallel to an axis of the vessel 810 with
the sensor locations along the sensing cable 101 generally
correspond to locations along a vertical axis within the vessel
810, such as along an inside wall of the vessel 810. Moreover, as
shown in FIG. 8, the sensing cable 101 can be arranged in a grid
pattern or array 911 and 912, or any other suitable pattern, about
a surface of the wash bed 820 or otherwise within the vessel 810.
One of ordinary skill in the art will also appreciate that more
than one sensing cable can be employed. For example, as depicted in
FIG. 8, a second sensing cable 910, which can also be positioned in
a grid pattern, can be positioned on an opposite surface of the
wash bed 820.
[0080] As previously noted, the sensing cable 101 includes a
heating/cooling element 103, such as a heating wire, and an optical
fiber sensor array 102, as disclosed herein. The optical fiber
includes a plurality of sensing locations along the length of the
fiber, such that each sensing location corresponds to a position
about the surface of the wash bed 820. For example, and as
previously noted, the optical fiber can include a plurality of
sensors along its length and/or a single fiber sensor can be
movable to define a plurality of sensor locations. The optical
fiber sensor is coupled to an optical signal interrogator 104 to
process an optical signal therein to obtain temperature
measurements at each of the sensor locations. The optical signal
interrogator 104 can further be coupled to a control unit 106 to
process the temperature measurements.
[0081] As previously described herein, the heating wire is coupled
to an excitation source 105 adapted to propagate electromagnetic
waves (e.g., current 210) through the heating wire, thereby
creating corresponding heat pulses (e.g., heat pulse 220). As the
heat pulses propagate through the heating wire, heat is exchanged
between the heating wire, the sensing cable, and the surrounding
media at each sensor location. The temperature at each sensor
location can be recorded, e.g., via the optical signal interrogator
and control unit, to generate a temperature profile for each sensor
location. For example, temperature can be measured as a function of
time at each sensor location along the optical fiber. The
temperature profile at each sensor location generally will
correspond to the characteristics of the medium surrounding the
sensing cable at that sensor location. In this manner, for purpose
of illustration, sensor locations over which fluid in the vessel
810 is flowing can result in a temperature profiles distinguishable
from sensor locations over which fluid is not flowing.
[0082] The temperature profile (i.e., the temperature as a function
of time at a sensor location) can generally exhibit an increase in
temperature coinciding with the exposure to the heat pulse at the
corresponding sensor location. For purpose of illustration, and not
limitation, and with reference to the laws of thermodynamics, the
temperature will generally increase over the duration of the heat
pulse at a rate corresponding to the characteristics of the
surrounding media, and thereafter decrease as the heat from the
heat pulse diffuses into the surrounding media at a rate
corresponding to the characteristics of the surrounding media.
Thus, the temperature profiles for each sensor location can
correspond to the characteristics of the surrounding media, e.g.,
the rate of flow of the surrounding media. For example, and not
limitation, at a sensing location over which the surrounding fluid
has a substantial flow, the heat transfer from the heating wire
into the surrounding media can be relatively high due to convective
heat transfer arising from the flow, and thus a cold spot/region
can be detected. By contrast, at a sensing location exposed to
stationary media, the heat transfer from the heating wire into the
surrounding media can be relatively low due to the lack of
convective heat transfer, and thus a hot spot/region can be
detected. That is, for purpose of illustration, and with reference
to Equation 1 and Equation 3, heat loss at a particular sensor
location can depend on the rate of flow of the fluid surrounding
that sensor location due to convective heat transfer from the
sensing cable into the surrounding fluid. Additionally, assuming a
homogenous medium of constant temperature flowing within the
component, the flow rate of the medium can be determined at each
sensor location. Moreover, assuming a medium having a non-uniform
temperature and substantially constant flow across the sensing
cable, the temperature of the medium without heating pulse can be
measured first, follow by measurement of the temperature of the
medium with heating pulse. The difference between the temperature
measurement without the heating pulse and the temperature
measurements with the heating pulse can indicate the flow rate of
the medium.
[0083] For purpose of illustration, and not limitation, reference
will be made to an example of the method disclosed herein with
reference to FIG. 7. FIG. 7 includes an image 1210 of a sensing
cable 1211 embedded between two layers of packing material. The
sensing cable 1211 can include an optical fiber sensor array
adjacent a heating wire. A water stream can be arranged to flow
through a portion of the packing material (e.g., from the top
layer, over the sensing cable 1211, and through the bottom layer).
As depicted in the image 1210 of FIG. 7, the water stream is
initially directed through the packing material at a location
approximately corresponding to 10-20 cm along the sensing cable
1211. As a heat pulse propagates through the heating wire, heat is
exchanged between the heating wire, the sensing cable 1211, the
surrounding packing material, air, and the water stream flowing
over the sensing cable 1211. During heating, overall temperature
readings at each sensor location increase, and the temperature
profile reveals the location of the water stream. For example, FIG.
7 includes a plot 1220 of temperature (z-axis) versus sensor
location in meters (x-axis) as a function of time (y-axis). Plot
1220 shows a trough of cooler temperature profiles corresponding to
the water stream due to convective heat loss. The region 1223 of
plot 1220 corresponds to the sensor locations along the sensing
cable 1221 exposed to air and outside packing material, and
illustrates a relatively higher temperature profile due to lack of
convective heat loss. As depicted in FIG. 7, at approximately 400
seconds, the water stream was moved back and forth about the
sensing cable 1211. As illustrated by plot 1220, wherever the water
flow passes over the sensing cable 1221, the temperature profiles
at corresponding sensor locations 1222 will be lower. The "Z"
pattern represents a cold temperature region can is caused by the
water stream moving back and forth.
[0084] As disclosed herein, the control unit thus can be adapted to
determine the characteristics of the surrounding media at each
sensor location using a variety of techniques, and thereby
determine the flow distribution of a fluid through a component. For
example, referring again to FIG. 6, the control unit 106 can be
adapted to determine, with reference to the known positions of the
sensor locations and the corresponding temperature profiles, a
relative rate of flow at each sensor location and thus determine
the flow distribution of the media surrounding the sensing cable.
In connection with the operation of a VPS distillation tower 810,
for example, vapor 1110 can flow upwards through one or more wash
beds 820 such that different fractions (i.e., different
petrochemicals in the vapor) can be separated. However, during
operation, coking can occur on the wash bed, which can create
uneven flow of vapor 1110 through the tower 810. Accordingly, the
methods disclosed herein can determine the flow distribution of the
vapor 1110 and thus detect a maldistribution condition associated
with coking. VGO wash oil 1120 can be introduced into the VPS
distillation tower 810 to prevent the formation of coke deposits,
for example upon detection of a coking condition. The methods
disclosed herein can likewise determine the flow rate and
distribution of the wash oil 1120.
[0085] For purpose of illustration, and not limitation, the direct
temperature measurement techniques described above can be used to
determine the flow distribution of a fluid through a component.
Particularly, a feature temperature profile (e.g., including three
temperature measurements corresponding to a heating period, a peak
temperature measurement, and a cooling period) can be extracted and
processed to determine characteristics of the medium surrounding
each sensor location. For example, and as depicted in FIG. 7, the
temperature profile of sensors exposed to a medium having a flow
characteristic can have a relative low peak, heating, and cooling
temperature relative to the temperature profile of sensors exposed
to a stationary medium of the same kind.
[0086] Alternatively, and as described herein with reference to
FIG. 4B, a log-time regression technique can be used to determine
certain characteristics of the medium surrounding each sensor
location by further processing the temperature profile at each
sensor location. That is, by performing the regression of the
temperature over log of time over an interval of time corresponding
to each heat pulse for each sensor location, the resulting slope
and intercept of the regression can be used to identify
characteristics of the medium. For example, the slope and intercept
of sensor locations exposed to a medium having a flow
characteristic can be distinguishable from the slope and intercept
of sensor locations exposed to the same medium having a stationary
characteristic.
[0087] In accordance with another exemplary embodiment of the
disclosed subject matter, the frequency spectrum techniques
disclosed herein with reference to FIG. 5A-C can be employed to
determine the flow distribution of a fluid through a component with
increased measurement sensitivity, accuracy, and/or reliability. In
this exemplary embodiment, and as described above, an N-pulse train
can be propagated through the heating wire of the sensing cable 101
with pre-selected parameters, including heating cycle period,
t.sub.0, number of heating cycles, N, and current amplitude,
I.sub.0. The parameters can be selected according to the operating
characteristics of the component such that the resulting
temperature profile can be measured with a desired signal-to-noise
ratio. For example, a longer heating cycle period or higher current
amplitude can result in higher signal-to-noise ratio relative to a
shorter heating cycle period or lower current amplitude. Likewise,
an increase in the number of heating cycles can further increase
the signal-to-noise ratio. One of ordinary skill in the art will
appreciate that such parameters can be varied depending upon
desired application. For example, if determination of flow
distribution is desired at short time intervals, a shorter heating
cycler period and a higher current amplitude can be employed. For
purpose of example, and not limitation, in connection with a fixed
bed reactor or VPS distillation tower having a diameter of
approximately 20 to approximately 40 feet, approximately 4 to 5
layers of wash bed packing materials, and a total height of
approximately 6 to approximately 10 feet. The heating cycle period
for the sensing cable can be approximately 1 Hz or slower (i.e. the
excitation source can be adapted to deliver a current pulse at 1 Hz
or slower. The current amplitude can be several mili-amperes to
several amperes. One of ordinary skill in the art will appreciate
that, in accordance with the disclosed subject matter, suitable
frequency and current amplitude can be determined for a particular
application by routine testing in accordance with known
methods.
[0088] The optical signal interrogator 104 can be adapted to
measure temperatures from the optical fiber at a pre-selected
sampling frequency. In accordance with an exemplary embodiment, the
sampling frequency can be at least twice the expected frequency of
the temperature profile and/or heat pulse. For example, and not
limitation, in connection with a fixed bed reactor or VPS
distillation tower, the sampling frequency can be 10 Hz. The
derivative with respect to time of the temperature measurements for
each sensor location can then be generated. For example, the
measured temperatures a sensor location at each sampling interval
can be given as a temperature series. The difference between each
temperature in the series can then be calculated to generate a
temperature derivative series. A transform (e.g., a FFT or DFT) can
be applied to convert the temperature derivative series into the
frequency domain, and thus generate a spectrum of time series of
temperature differences for each sensor location. The derivative of
the spectrum, with respect to the frequency, can be generated. That
amplitude and phase of the frequency-derivative spectrum (e.g., the
real and imaginary parts of the complex frequency-derivative
spectrum) can then be determined. For example, using the heating
cycle period, t.sub.0, the real and imaginary values of the
spectrum at the fundamental frequency of the N-pulse train can be
selected at f.sub.0=1/t.sub.0.
[0089] The amplitude and phase of the frequency-derivative spectrum
at each sensor location thus can correspond to the characteristics
of the medium surrounding the sensing cable 101 at a particular
sensor location. For example, the amplitude and phase can decrease
monotonically with frequency so that higher frequency corresponds
with lower response to a change in temperature from the heating
element. Accordingly, lower frequencies can obtain significant
heating response and higher signals. Additionally, the imaginary
part of the complex spectrum can be nearly linear with the
frequency while the real part can exhibit linear behavior beyond
certain frequency values. Therefore, the derivative of the transfer
function spectrum with respect to frequency can correspond to the
linear relationship of the temperature change with log(t) in the
time domain. In this manner, the amplitude and phase of sensor
locations exposed to a flowing medium can be distinguishable from
the amplitude and phase of sensor locations exposed to non-flowing
medium of the same kind, or a higher-velocity flowing medium from a
lower-velocity flowing medium.
[0090] The sensing cable 101 can be calibrated, e.g., with the
control unit. Calibration can include, for example, calibrating the
sensor array to determine the amplitude and phase of the
frequency-derivative spectrum of certain known media. For example,
a number of materials with known thermal properties can be measured
for a broad range of values and for a broad range of flow rates,
and a database can be constructed including correlations between
the generated amplitude and phase and characteristics, such as flow
rate, of the known materials. The database can then be used as to
determine the flow rate of the surrounding medium at a particular
sensor location in the vessel.
[0091] The control unit 106, with reference to the known locations
of each sensor and the corresponding amplitude and phase of the
frequency-derivative spectrum, can determine the flow distribution
of a fluid through the component. To determine the flow
distribution, the control unit can be configured to store the known
position of each sensor location in one or more memories. For
example, for a 36 inch long sensing cable, having 36 sensor
locations each spaced apart by a unit inch, positioned about the
surface of a 36 inch wash bed 820, the control unit can store the
distance of each sensor location from the wall of the component 810
(i.e., for sensor location i=1, 2, . . . , 36), the control unit
can store a corresponding distance measurement D.sub.i={1 in, 2 in,
. . . , 36 in}). For each sensor location, i, the control unit can
determine the amplitude and phase of the frequency derivative
spectrum as disclosed herein. With reference to, for example, a
database storing the amplitude and phase of the frequency
derivative spectrum for known flow rates of the known media, the
control unit can thus determine the relative flow rate at each
sensor location and thus the flow distribution using the determined
amplitude and phase at each sensor location.
[0092] Additionally or alternatively, and as embodied herein, the
control unit can process the determined amplitude or phase of the
frequency derivative spectrum of adjacent sensor locations to
determine the flow distribution. That is, for example, assuming the
vessel contains media with otherwise constant characteristics, a
change in the amplitude across two sensor locations can correspond
to a different flow rate across the two sensor location. Likewise,
a change in the phase can correspond to a different flow rate of
the same media. In certain embodiments, the control unit can
process both the amplitude and phase of adjacent sensors to enhance
determination of flow distribution. For example, a change in both
the amplitude and phase can correspond a different flow rate across
the two sensors. Moreover, in certain embodiments, the control unit
can monitor the amplitude and phase of each sensor location over
time (e.g., throughout the operation of a VPS distillation tower)
and determine whether the temperature profile of one or more sensor
locations changes with time. For example, the control unit can be
configured to monitor the temperature profile of one or more sensor
locations over time, identify a change in said temperature profile
and, with reference, e.g., to a database of known characteristics
corresponding to flow rate, determine the flow distribution.
[0093] In another exemplary embodiment, multiple layers of sensors
can be deployed between different layers of packing materials, for
example as depicted in FIG. 8. Measurement from each layer of
sensor can reveal localized conditions, such as the flow rate at
each sensor location. In this manner, entrainment of resid can be
inferred by comparison of measurement results across sensor
layers.
[0094] The techniques disclosed herein can provide for continuous
determination of flow distribution through a component. No moving
mechanical parts need be included inside the sensing cable. Because
material thermal properties can be measured for determination of
flow distribution, the measurement results can be independent of
electrical conductivity, salinity, and crude oil constituents, such
as sulfur, iron sulfide/oxide. Moreover, relative temperature
changes before and after heating/cooling can be used to infer
material thermal properties for determination of flow distribution,
and temperature baseline can be taken each time before
heating/cooling is applied. Accordingly, the methods disclosed
herein need not require long term stability for temperature
sensors.
[0095] Moreover, the system disclosed herein can operate at
temperatures ranging from cryogenic temperatures up to over
1000.degree. C. The size of the sensing cable can be relatively
small (e.g., compared to conventional thermocouples) and can be
cost effective for large area coverage with a large amount of
sensors. Utilizing cost-effective optical fiber temperature
sensors, the system disclosed herein can incorporate a large number
of sensors, and can offer a high spatial resolution, e.g., less
than 1 mm, over a long measurement range, e.g., several meters to
kilometers. The diameter of the compact sensing cable can small,
e.g., less than 2 mm. The small diameter of the sensing cable can
allow for measurement in a tight space with reduced intrusiveness.
Furthermore, the heating/cooling element can be turned off, and the
sensing cable can be converted to a temperature sensor, which can
provide absolute temperature measurements inside the vessel, such
as measurements of the wash bed packing materials. Such absolute
temperature measurements can be used to infer liquid/vapor
distributions, for example, inside packing materials, where
temperature differences between liquid and vapor.
[0096] Based upon the above, for purpose of illustration and not
limitation, systems and methods are provided in accordance with the
disclosed subject matter for detecting a leak in a pipeline or
similar component. As embodied herein, the systems methods herein
include providing along a length of a perimeter of a wall of a
pipeline a sensing cable including an optical fiber sensor array
aligned with a heating element. The method includes propagating at
least one heat pulse through the heating element along at least a
portion of the sensing cable to affect an exchange of thermal
energy between the heating element and fluid exposed to the sensing
cable. The method includes measuring, over time, a temperature
profile of the sensing cable corresponding to the heat pulse at
each of a plurality of sensor locations on the optical fiber sensor
array. The method includes detecting a leak in a pipeline by
determining one or more properties of the fluid exposed to the
sensing cable at each of the plurality of sensor locations based on
the temperature profile corresponding thereto.
[0097] For purpose of illustration and not limitation, reference is
made to the exemplary systems and methods for detecting a leak in a
pipeline with reference to FIGS. 9-12. In accordance with certain
embodiments, the techniques described herein for measuring a
characteristic of one or more materials and determining the flow
distribution of a fluid through a component can be used, either
alone or in combination, for detecting a leak in a pipeline. For
example, and in accordance with certain embodiments, the system for
detecting a leak in a pipeline can include the components and
features described herein with reference to FIG. 1A-C.
[0098] With reference now to FIG. 9, for purpose of illustration
and not limitation, a sensing cable (e.g., sensing cable 101)
including an optical fiber sensor array 102 can be provided along a
length of a perimeter of a wall of a pipeline 9900. Using the
systems and techniques as disclosed, and suitable modifications as
desired, a method of detecting a leak in the pipeline 9900 includes
propagating at least one heat pulse 220 through a heating element
(e.g., heating element 103) to affect an exchange of thermal energy
between the heating element and the fluid exposed to the sensing
cable. A temperature profile of the sensing cable corresponding to
the heat pulse 220 at each of a plurality of sensor locations is
measured, over time, as described herein. A leak 9909 in the
pipeline 9900 thus can be detected by determining one or more
properties of the fluid exposed to the sensing cable at one or more
sensor locations based on the temperature profiles corresponding to
the sensor locations.
[0099] As previously noted, the sensing cable 101 includes a
heating/cooling element 103, such as a heating wire. The optical
fiber includes a plurality of sensing locations along the length of
the fiber, such as discrete sensor locations disposed along the
optical fiber, or by the optical fiber itself. Each sensing
location corresponds to a position along and/or about length of the
perimeter of the wall of the pipeline 9900. The optical fiber
sensor is coupled to an optical signal interrogator 104 to process
an optical signal therein to obtain temperature measurements at
each of the sensor locations. The optical signal interrogator 104
can further be coupled to a control unit 106 to process the
temperature measurements. As depicted schematically in FIG. 9, the
sensing cable can be provided along an axial length of the
perimeter of the wall of the pipeline 9990. In this manner, a leak
9909 in the pipeline 9900 can be detected along the axial length of
the pipeline. For example, as illustrated by plot 9950, the signal
interrogator 104 can be adapted to receive an optical signal from
which a temperature profile at each sensor location along the axial
length of the pipeline 9900 can be measured. Alternatively, the
sensing cable can be disposed circumferentially along a wall of the
pipeline 9900, to detect a leak along the circumference of the
pipeline, or other arrangements as desired. As embodied herein, the
sensing cable can be provided along an inner or outer wall of the
pipeline.
[0100] Additionally, and in accordance with certain embodiments,
the sensing cable (e.g., sensing cable 101) can further include
features suitable for deployment along a perimeter of a wall of a
pipeline. For example, with reference to FIGS. 10A and 10C, the
sensing cable can include an outer diameter including a polymer
sheath 1001. The polymer sheath 1001 can protect the sensing cable
from hash or corrosive environments such as, for example and in
connection with a sensing cable aligned along an outer wall of a
subsea pipeline, sea water. The sensing cable can further include a
power cable 1003 for optical signal amplification. For purpose of
illustration, and not limitation, for applications involving a long
sensing cable (e.g., longer than 40 km), a power cable 1003 can be
included for amplification of optical signals passing through the
optical fibers 102. In certain embodiments, a layer of insulation
1004 can be provided around the power cable 1003 to prevent or
mitigate interference from heat generated by the power cable 1003.
The sensing cable can further include one or more armoring wires
(e.g., 1002a and 1002b [collectively, 1002]). In certain
embodiments, the armoring wires 1002 can be formed from steel or
the like to provide reinforcement to the sensing cable.
[0101] The sensing cable as depicted herein further includes a
heating element 103 such as a resistive heating element. As
described herein with reference to FIGS. 1A-C, the heating element
103 can be aligned either adjacent or concentric to the optical
fiber sensor array 102. FIG. 10A depicts an embodiment of the
disclosed subject matter with the heating element 103 arranged
concentrically around the optical fiber sensor array 102. For
purpose of illustration and not limitation, the heating element 103
can include a copper heating wire. Additionally or alternatively,
one or more of the armoring wires 1002, aligned adjacent with the
optical fiber sensor array 102, can be used as the heating element
103. Also as described herein with reference to FIG. 1A-C, the
optical fiber sensor array 102 and optical signal interrogator 104
can include fiber Bragg grating array based sensing, Raman
scattering based sensing, Rayleigh scattering based sensing, or
Brillioun scattering based sensing, as desired depending upon the
intended application. For example, a sensing system can be selected
based on, among other considerations appreciated by those of
ordinary skill in the art, the spatial and temporal resolutions and
cable length constraints provided in Table I.
[0102] As previously described herein, the heating wire is coupled
to an excitation source 105 adapted to propagate electromagnetic
waves (e.g., current 210) through the heating wire, thereby
creating corresponding heat pulses (e.g., heat pulse 220). As the
heat pulses propagate through the heating wire, heat is exchanged
between the heating wire, the sensing cable, and the surrounding
media along the sensing cable at each sensor location. The
temperature at each sensor location can be recorded, e.g. via the
optical signal interrogator and control unit, to generate a
temperature profile for each sensor location. For example,
temperature can be measured as a function of time at each sensor
location along the optical fiber. The temperature profile at each
sensor location generally will correspond to the characteristics of
the medium surrounding the sensing cable at that sensor location.
In this manner, for purpose of illustration, sensor locations
proximate or exposed to fluid leaking from the pipeline can result
in temperature profiles distinguishable from sensor locations
exposed to other media as described herein with reference to FIGS.
1-5. Likewise, sensor locations over which fluid leaking from the
pipe flows can result in a temperature profiles distinguishable
from sensor locations over which fluid is not flowing as described
herein with reference to FIGS. 6-8.
[0103] For purpose of illustration, and not limitation, certain
exemplary embodiments of systems and methods for detecting a leak
in a pipeline are provided with reference to FIGS. 11 and 12. In
certain embodiments, detecting the leak 9909 in the pipeline 9900
can include comparing a difference in the one or more properties of
fluid exposed to the sensing cable between adjacent sensor
locations. For example, FIG. 12 depicts a schematic of a sensing
cable including heating element 103 and optical fiber sensor array
102 aligned axially along a pipeline 9900 residing on the sea
floor. In connection with this embodiment, the sensing cable at
each sensing location along the optical fiber sensor array is
exposed to seawater 1290 in the absence of a leak. Without the
leak, the one or more determined properties based on the
temperature profile at each sensor location generally can be
similar across all and adjacent sensor locations as illustrated by
plot 1270.
[0104] By contrast, in the presence of a leak 9909 one or more
sensor locations of the optical fiber sensor array 102 aligned
along an axial length of the pipeline 9900 will be exposed to fluid
flowing from the leak 9909. The one or more determined properties
based on the temperature profile at sensor locations proximate or
exposed to the leak 9909 can be distinguishable from those at
sensor locations exposed to seawater 1290. Plot 1280 schematically
illustrates a difference 1285 between the thermal properties of the
leaking fluid exposed to the sensing cable at sensor locations
corresponding to the leak 9909 and the thermal properties of the
seawater 1290 exposed to the sensing cable at other sensing
locations. As embodied herein, the determined properties of the
fluid exposed to the sensing cable can relate to, without
limitation, the thermal conductivity of the fluid and/or the flow
rate of the fluid as previously described.
[0105] The difference in the one or more properties of fluid
exposed to the sensing cable between adjacent sensor locations can
thus indicate a leak between adjacent sensor locations. One of
skill in the art will appreciate that the measurements disclosed
herein can include a margin of error, which can depend on, among
other things, the type of sensing system utilized and the
environment in which it is located. Accordingly, in certain
embodiments, a threshold indicating a leak between adjacent sensor
locations can be determined based on these factors, the operating
conditions, and/or calibration.
[0106] Additionally or alternatively, and using the technique as
described herein, determining the one or more properties of the
fluid exposed to the sensing cable at each of the plurality of
sensor locations can include comparing the temperature profile at
one or more selected sensor locations to one or more predetermined
temperature profiles, wherein each predetermined temperature
profile can relate to a fluid with one or more predetermined
properties. For purpose of illustration, with reference to FIG. 11,
the temperature profile at each sensor location, as illustrated by
plot 1190, can correspond to the temperature characteristics of the
surrounding media. For example, sensing cable can be exposed to
water 1181, oil 1182, and gas 1183. Assuming each medium is stable
around the sensing cable, the rate of heat exchange, and thus the
temperature profiles 1191, 1192, and 1193, between the sensing
cable and the surrounding media at each sensor location can
correspond to the heat conduction of the surrounding media. That
is, for example, heat transfer between the sensing cable and
surrounding gas 1183 can be lower than that between the sensing
cable and water 1181, as water has a higher heat conduction.
Similarly, with knowledge of the media's conductive thermal
properties, the temperature profiles can correspond to the heat
convection (e.g., flow rate) of the surrounding media at each
sensor location. That is, for example, heat transfer between the
sensing cable and stationary surrounding seawater can be lower than
that between the sensing cable and a fluid flowing over the sensing
cable.
[0107] Again with reference to FIG. 12, a first predetermined
property can also relate to a fluid within the pipeline 9900. For
example, the first predetermined property can relate to the heat
conduction or heat capacity of the fluid within the pipeline, and
can be determined by calibration using the techniques herein. That
is, for example, a material with one or more known properties can
be exposed to one or more sensor locations and the measured
temperature profile corresponding thereto can be recorded. During
operation, the temperature profiles at the sensor locations can be
monitored. Identification of a temperature profile corresponding to
the first predetermined property related to the fluid within the
pipeline 9900 can thus indicate a leak 9909. Additionally or
alternatively, a second predetermined property can relate to flow
rate. For example, the second predetermined property can relate to
the flow rate of a known fluid within the pipeline. That is, for
example, a known fluid can be exposed to one or more sensor
locations at varying flow rates and the measured temperature
profiles corresponding thereto can be recorded. During operation,
the temperature profiles at the sensor locations can be monitored.
Identification of a temperature profile corresponding to the second
predetermined property related to a high flow rate can thus
indicate a leak.
[0108] The techniques disclosed herein can provide for detection of
a leak in a pipeline. No moving mechanical parts need be included
inside the sensing cable. Because material thermal properties can
be measured for detection of a leak in the pipeline, the
measurement results can be independent of electrical conductivity,
salinity, and crude oil constituents, such as sulfur, iron
sulfide/oxide. Moreover, relative temperature changes before and
after heating/cooling can be used to infer material thermal
properties for detection of a leak in a pipeline, and a temperature
baseline can be taken each time before heating/cooling is applied.
Accordingly, the methods disclosed herein need not require long
term stability for temperature sensors.
[0109] The techniques disclosed herein can provide a wide range of
sensing applications, including both short and long range sensing.
The techniques disclosed herein can provide continuous monitoring
with improved sensing capability, and in addition to pipeline leak
detection for both liquid and gas, can further include sensing of
biological fouling location and growth, flow assurance monitoring,
liquid level/interface identification, and/or liquid/gas flow
profiling. Use of optical fiber sensors can be safe,
non-conductive, lightweight, low power, high sensitivity, and can
be insensitive to electromagnetic radiation.
[0110] Moreover, due to the varying thermal conductivities of
different media typically involved in pipeline operations, the
systems and methods disclosed herein can provide for the detection
of specific fluids through calibration. The systems and methods
disclosed herein can provide improved leak detection capability,
including continuous monitoring with improved sensing
capability.
Additional Embodiments
[0111] Additionally or alternately, the invention can include one
or more of the following embodiments.
Embodiment 1
[0112] A method for detecting a leak in a pipeline, comprising:
providing along a length of a perimeter of a wall of a pipeline a
sensing cable including an optical fiber sensor array aligned with
a heating element; propagating at least one heat pulse through the
heating element along at least a portion of the sensing cable to
affect an exchange of thermal energy between the heating element
and fluid exposed to the sensing cable; measuring, over time, a
temperature profile of the sensing cable corresponding to the heat
pulse at each of a plurality of sensor locations on the optical
fiber sensor array; and detecting a leak in a pipeline by
determining one or more properties of the fluid exposed to the
sensing cable at each of the plurality of sensor locations based on
the temperature profile corresponding thereto.
Embodiment 2
[0113] The method of any of the previous embodiments, wherein the
sensing cable is provided along an axial length of the perimeter of
the wall of the pipeline.
Embodiment 3
[0114] The method of any of the previous embodiments, wherein the
sensing cable further includes an outer diameter including a
polymer sheath.
Embodiment 4
[0115] The method of any of the previous embodiments, wherein the
sensing cable further includes a power cable for optical signal
amplification.
Embodiment 5
[0116] The method of any of the previous embodiments, wherein the
sensing cable includes one or more steel armouring wires.
Embodiment 6
[0117] The method of any of the previous embodiments, wherein the
heating element comprises at least one of the one or more steel
armouring wires.
Embodiment 7
[0118] The method of any of the previous embodiments, wherein the
heating element includes a resistive heating element and wherein
propagating the at least one heat pulse includes applying an
electrical pulse with a predetermined frequency and predetermined
waveform.
Embodiment 8
[0119] The method of any of the previous embodiments, wherein the
heating element includes a copper heating wire.
Embodiment 9
[0120] The method of any of the previous embodiments, wherein
propagating at least one heat pulse through the heating element
includes propagating the at least one heat pulse through a heating
element aligned adjacent to the optical fiber sensor array.
Embodiment 10
[0121] The method of any of the previous embodiments, wherein
propagating at least one heat pulse through the heating element
includes propagating the at least one heat pulse through a heating
element disposed concentrically with the optical fiber sensor
array.
Embodiment 11
[0122] The method of any of the previous embodiments, wherein
measuring, over time, the temperature profile includes measuring
using fiber Bragg grating array based sensing, Raman scattering
based sensing, Rayleigh scattering based sensing, or Brillioun
scattering based sensing.
Embodiment 12
[0123] The method of any of the previous embodiments, wherein
detecting the leak in the pipeline includes comparing a difference
in the one or more properties of fluid exposed to the sensing cable
between adjacent sensor locations, and wherein the difference
indicates a leak between adjacent sensor locations if the
difference exceeds a predetermined threshold.
Embodiment 13
[0124] The method of any of the previous embodiments, wherein
determining the one or more properties of the fluid exposed to the
sensing cable at each of the plurality of sensor locations includes
comparing the temperature profile at each of the plurality of
sensor locations to one or more predetermined temperature profiles,
wherein each predetermined temperature profile relates to a fluid
with one or more predetermined properties.
Embodiment 14
[0125] The method of any of the previous embodiments, wherein at
least a first predetermined property relates to a fluid within the
pipeline, and wherein detecting the leak in the pipeline includes
identifying, at one or more of the plurality of sensor locations, a
temperature profile corresponding to the first predetermined
property.
Embodiment 15
[0126] The method of any of the previous embodiments, wherein at
least a second predetermined property relates to flow rate, and
wherein detecting the leak in the pipeline includes identifying, at
one or more of the plurality of sensor locations, a temperature
profile corresponding to the second predetermined property.
Embodiment 16
[0127] A system for detecting a leak in a pipeline, comprising: a
sensing cable including an optical fiber sensor array aligned with
a heating element disposed along a length of a perimeter of a wall
of a pipeline, the optical fiber sensor array having a plurality of
sensor locations; an excitation source coupled with the heating
element and configured to propagate at least one heat pulse through
the heating element along at least a portion of the sensing cable
to affect an exchange of thermal energy between the heating element
and fluid exposed to the sensing cable; an optical signal
interrogator coupled with the optical fiber sensor array and
adapted to receive a signal from each of the plurality of sensor
locations and configured to measure, over time, a temperature
profile of the sensing cable corresponding to the heat pulse at
each of the plurality of sensor locations on the optical fiber
sensor array; and a control unit, coupled with the heating element
and the optical signal interrogator, to detect a leak in the
pipeline by determining one or more properties of the fluid exposed
to the sensing cable at each of the plurality of sensor locations
based on the temperature profile corresponding thereto.
Embodiment 17
[0128] The system of embodiment 16, wherein the sensing cable is
disposed along an axial length of the perimeter of the wall of the
pipeline.
Embodiment 18
[0129] The system of embodiment 16 and/or 17, wherein the sensing
cable further includes an outer diameter including a polymer
sheath.
Embodiment 19
[0130] The system of embodiment 16, 17 and/or 18, wherein the
sensing cable further includes a power cable for optical signal
amplification.
Embodiment 20
[0131] The system of embodiment 16, 17, 18 and/or 19, wherein the
sensing cable includes one or more steel armouring wires.
Embodiment 21
[0132] The system of embodiment 16, 17, 18, 19, and/or 20, wherein
the heating element comprises at least one of the one or more steel
armouring wires.
Embodiment 22
[0133] The system of embodiment 16, 17, 18, 19, 20, and/or 21,
wherein the heating element includes a resistive heating element
and wherein the excitation source is configured to propagate an
electrical pulse with a predetermined frequency and predetermined
waveform, the electrical pulse corresponding to the at least one
heat pulse.
Embodiment 23
[0134] The system of embodiment 16, 17, 18, 19, 20, 21, and/or 22,
wherein the heating element includes a copper heating wire.
Embodiment 24
[0135] The system of embodiment 16, 17, 18, 19, 20, 21, 22, and/or
23, wherein the heating element is aligned adjacent to the optical
fiber sensor array.
Embodiment 25
[0136] The system of embodiment 16, 17, 18, 19, 20, 21, 22, 23,
and/or 24, wherein the heating element is disposed concentrically
with the optical fiber sensor array.
Embodiment 26
[0137] The system of embodiment 16, 17, 18, 19, 20, 21, 22, 23, 24,
and/or 25, wherein the optical fiber sensor array and the optical
signal interrogator include a fiber Bragg grating array based
sensing system, a Raman scattering based sensing system, a Rayleigh
scattering based sensing system, or a Brillioun scattering based
sensing system.
Embodiment 27
[0138] The system of embodiment 16, 17, 18, 19, 20, 21, 22, 23, 24,
25, and/or 26, wherein the control unit is configured to detect the
leak in the pipeline by comparing a difference in the one or more
properties of fluid exposed to the sensing cable between adjacent
sensor locations, and wherein the difference indicates a leak
between adjacent sensor locations if the difference exceeds a
predetermined threshold.
Embodiment 28
[0139] The system of embodiment 16, 17, 18, 19, 20, 21, 22, 23, 24,
25, 26, and/or 27, wherein the control unit is configured to
determine the one or more properties of the fluid exposed to the
sensing cable at each of the plurality of sensor locations by
comparing the temperature profile at each of the plurality of
sensor locations to one or more predetermined temperature profiles,
wherein each predetermined temperature profile relates to a fluid
with one or more predetermined properties.
Embodiment 29
[0140] The system of embodiment 16, 17, 18, 19, 20, 21, 22, 23, 24,
25, 26, 27, and/or 28, wherein at least a first predetermined
property relates to a fluid within the pipeline, and wherein the
control unit is configured to detect the leak in the pipeline by
identifying, at one or more of the plurality of sensor locations, a
temperature profile corresponding to the first predetermined
property.
Embodiment 30
[0141] The system of embodiment 16, 17, 18, 19, 20, 21, 22, 23, 24,
25, 26, 27, 28 and/or 29, wherein at least a second predetermined
property relates to flow rate, and wherein the control unit is
configured to detect the leak in the pipeline by identifying, at
one or more of the plurality of sensor locations, a temperature
profile corresponding to the second predetermined property.
[0142] While the disclosed subject matter is described herein in
terms of certain exemplary embodiments, those skilled in the art
will recognize that various modifications and improvements can be
made to the disclosed subject matter without departing from the
scope thereof. Moreover, although individual features of one
embodiment of the disclosed subject matter can be discussed herein
or shown in the drawings of the one embodiment and not in other
embodiments, it should be apparent that individual features of one
embodiment can be combined with one or more features of another
embodiment or features from a plurality of embodiments.
[0143] In addition to the specific embodiments claimed below, the
disclosed subject matter is also directed to other embodiments
having any other possible combination of the dependent features
claimed below and those disclosed above. As such, the particular
features presented in the dependent claims and disclosed above can
be combined with each other in other manners within the scope of
the disclosed subject matter such that the disclosed subject matter
should be recognized as also specifically directed to other
embodiments having any other possible combinations. Thus, the
foregoing description of specific embodiments of the disclosed
subject matter has been presented for purposes of illustration and
description. It is not intended to be exhaustive or to limit the
disclosed subject matter to those embodiments disclosed.
[0144] It will be apparent to those skilled in the art that various
modifications and variations can be made in the method and system
of the disclosed subject matter without departing from the spirit
or scope of the disclosed subject matter. Thus, it is intended that
the disclosed subject matter include modifications and variations
that are within the scope of the appended claims and their
equivalents.
* * * * *